Formation of Metal-Poor Globular Clusters in Cold Streams

In Mandelker et al 2018, we proposed that cold filamentary accretion in high-z galaxies can lead to the formation of star-forming clumps in the CGM without associated dark-matter substructure, and that these clumps could be the birth places of metal-poor globular clusters (MP GCs), whose formation had long been a mystery. I derived an analytic model for the properties of streams as a function of halo mass and redshift, assessed when streams would be gravitationally unstable, when this could lead to star-formation in the halo, and when it may result in GC formation. This was found to be possible at z>~4.5, particularly in the turbulent “eyewall” at ~0.3Rv where stream collisions can drive very large densities. My model can account for numerous observed properties of GC systems, and the prediction that GCs form along circumgalactic filaments at high-redshift will be testable with JWST.


Galaxy formation in the cosmic web. Shown is gas column density in a ~2x10^{11} solar mass  halo at z~6 from the VELA simulations, integrated over 40 kpc. Solid and dashed grey circles mark the virial radius, Rv, and 0.3Rv. Left: Cold streams feeding the halo from the cosmic web. Right: In the inner halo, the streams can fragment into dense, star-forming clumps (black circles), possibly leading to metal-poor globular clusters, while accretion onto the disk drives VDI. Adapted from Mandelker et al. 2018